We thank Gabriel Ahlfeldt, Pierre-Philippe Combes, Kerem Cosar, Don Davis, Jonathan Dingel, Gilles Duranton, Fabian Eckert, Pablo Fajgelbaum, James Feigenbaum, Ed Glaeser, Laurent Gobillon, Gordon Hanson, Miklos Koren, Hans Koster, Oleg Itskhoki, Guy Michaels, Eduardo Morales, Henry Overman, Javier Quintana, Steve Redding, Jean-Marc Robin, Michele Rosenberg, Esteban Rossi-Hansberg, Olmo Silva, Robert Staiger, Daniel Sturm, Lin Tian, Elisabet Viladecans-Marsal, Pablo Warnes, David Weinstein, as well as participants in seminars and conferences, e.g., at HU Berlin, Birmingham, Bocconi, Bologna, Bristol, BU, CERGE-EI, Chicago Fed, CRED, CREi, CURE, Dortmund, the EEA meetings, FREIT, Georgetown, HEC, Helsinki, INSEAD, LSE, McGill, NBER SI, Oregon, Oslo, Penn State, Philadelphia Fed, Princeton, PSE, Reading, Richmond Fed, RWI, Sciences-Po, SED, Sheffield, SMU, Toronto, Tufts, UCL, UCLA, UEA, UPF, USC, Virginia, Washington, Warwick, the World Bank, and York for useful comments. We would also like to thank Clement Gorin for invaluable advice and the Cambridge Group for the History of Population and Social Structure, the British Library, Alexis Litvine and Gethin Rees for their help with data. Heblich and Zylberberg acknowledge support from the ANR/ESRC/SSHRC, through the ORA grant ES/V013602/1 (MAPHIS: Mapping History). The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.